In general, an ink for a water-based ink ballpoint pen has such a low viscosity as 50 mPa·sec to 3 Pa·sec while that for an oil-based ink ballpoint pen having a similar form has a viscosity of 3 Pa·sec to 20 Pa·sec, and therefore when the pen is left standing upward or horizontally, the ink leaks out. Further, the ink is likely to be scattered by slight impact to stain hands and cloths, and therefore in order to prevent this, an ink follower is installed at a plug part in an ink reservoir.
A lot of ink followers which are blended with silica, metallic soap and a clay thickener as a viscosity controlling agent to increase a viscosity has so far been known.
However, ink followers blended with the above viscosity controlling agents are predominant in viscosity response, and therefore if they are used particularly for a water-based ink ballpoint pen of a bold type consuming a large amount of ink, brought about are the problems that starving of the drawn lines is induced in the middle of writing because of difficulty in following of the ink and that a part of an ink follower is adhered and remains on the inner wall of an ink reservoir in consuming the ink to result in causing shortage in the ink follower in the middle of writing to allow the ink to flow backward and a flow rate for writing becomes instable due to an influence of shortage in the ink follower. In the ballpoint pens of specifications other than the bold type, the same problems are brought about in a certain case when the writing speed is hastened.
Such problems are considered to originate in a slower following speed of an ink follower than a consuming speed of an ink.
Also, in an ink follower in which a viscosity is controlled to a lower level in order to improve the above problems, brought about are the problems that the follower and the ink are scattered when impact is applied to the pen body and that the ink follower flows out from the ink reservoir when the pen body is stored at a high temperature with the pen tip turned upward.
Further, known is an ink follower (called “a back leaking preventer” in a literature) blended with a hydrocarbon which is liquid at room temperature and a styrene base thermoplastic elastomer (for example, Japanese Patent No. 3016749).
However, in the ink follower (back leaking preventer) described in the above official gazette, the styrene base thermoplastic elastomer used is relatively high in a permanent distortion, a heat deformation and an elastic deformation with the passage of time, and therefore the ink follower itself is poor in stability with the passage of time. In particular, when writing is carried out after the pen body is left standing in a hot state of 30 to 50° C., a viscoelasticity of the ink follower is varied, and therefore a problem such as an extreme reduction in the ink flow rate are brought about.
In light of the conventional problems described above, the present invention intends to solve them, and an object thereof is to provide an ink follower which has stable followability regardless of a pen body specification, a flow rate for writing and a writing speed and does not cause back leaking of the ink originating in shortage of the ink follower in the middle of writing and scattering of the ink follower by impact applied to the pen body and which does not flow out from the ink reservoir in storing the pen body at a high temperature and provides a stable flow rate for writing. Also, it is a matter of course that provided is an ink follower which prevents the ink from volatilizing by shutting off the ink from the outside air (volatilization preventing property) and which prevents the ink from leaking in writing with the pen turned upward.